Remove -[no]implicit-objc-with.

Toggling this option causes funny things to happen, and there's no
point in keeping it.

Swift SVN r20565

lib/Frontend/CompilerInvocation.cpp

@@ -586,12 +586,6 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   Opts.EnableAppExtensionRestrictions |= Args.hasArg(OPT_enable_app_extension);
   Opts.SplitPrepositions |= Args.hasArg(OPT_split_objc_selectors);
 
-  if (auto A = Args.getLastArg(OPT_implicit_objc_with,
-                               OPT_no_implicit_objc_with)) {
-    Opts.ImplicitObjCWith
-      = A->getOption().matches(OPT_implicit_objc_with);
-  }
-
   if (Opts.SplitPrepositions)
     Opts.addBuildConfigOption("OBJC_SELECTOR_SPLITTING");